The present invention relates to a composition for film formation. More particularly, the invention relates to a composition for film formation which is capable of forming a silica-based coating film having low water absorption and dielectric constant of 2.1 or lower and useful as an interlayer insulating film material in semiconductor devices, etc.
Silica (SiO2) films formed by vacuum processes such as CVD have hitherto been used frequently as interlayer insulating films in semiconductor devices and other devices. In recent years, an insulating coating film which comprises a tetraalkoxysilane hydrolyzate as the main component and is called an SOG (spin on glass) film has come to be used for the purpose of forming a more even interlayer insulating film. Furthermore, as a result of the trend toward higher degree of integration in semiconductor devices and the like, an interlayer insulating film called an organic SOG film has been developed which comprises a polyorganosiloxane as the main component and has low dielectric constant.
In particular, with further progress in the degree of integration or multilayer constitution in semiconductor devices and the like, better electrical insulation between conductors has come to be required and, hence, an interlayer insulating film material having lower dielectric constant and lower water absorption has come to be desired.
Proposed as materials attaining low dielectric constant are a composition comprising a mixture of fine particles obtained by condensing an alkoxysilane in the presence of ammonia and a basic product of partial hydrolysis of an alkoxysilane (see Japanese Patent Laid-Open Nos. 263045/1993 and 315319/1993) and a coating fluid obtained by condensing a basic hydrolyzate of a polyalkoxysilane in the presence of ammonia (see Japanese Patent Laid-Open Nos.340219/1999 and 340220/1999). However, the materials obtained by these methods have considerable unevenness in film properties such as low water absorption and dielectric constant of 2.1 or lower because of the unstable properties of the reaction products. Consequently, these materials are unsuitable for industrial production.
One object of the invention is to provide a composition for film formation which eliminates the problem described above. More particularly, the object is to provide a composition for film formation which is capable of giving a silica-based coating film having low water absorption and low dielectric constant of 2.1 or lower and useful as an interlayer insulating film in semiconductor devices and the like.
Another object of the invention is to provide a silica-based film obtained from the composition.
The invention provides a composition for film formation which comprises:
(A) a product of hydrolysis and condensation obtained by hydrolyzing and condensing at least one silane compound selected from the group consisting of compounds represented by the following formula (1) (hereinafter referred to also as xe2x80x9ccompounds (1)xe2x80x9d), compounds represented by the following formula (2) (hereinafter referred to also as xe2x80x9ccompounds (2)xe2x80x9d), and compounds represented by the following formula (3) (hereinafter referred to also as xe2x80x9ccompounds (3)xe2x80x9d) in the presence of a basic catalyst and water,
RaSi(OR1)4xe2x88x92axe2x80x83xe2x80x83(1)
wherein R represents a hydrogen atom, a fluorine atom, or a monovalent organic group; R1 represents a monovalent organic group; and a is an integer of 1 or 2,
Si(OR2)4xe2x80x83xe2x80x83(2)
xe2x80x83wherein R2 represents a monovalent organic group,
R3b(R4O)3xe2x88x92bSixe2x80x94(R7)dxe2x80x94Si(OR5)3xe2x88x92cR6cxe2x80x83xe2x80x83(3)
xe2x80x83wherein R3 to R6 may be the same or different and each represents a monovalent organic group; b and c may be the same or different and each is a number of 0 to 2; R7 represents an oxygen atom, a phenylene group, or a group represented by xe2x80x94(CH2)nxe2x80x94, wherein n is an integer of 1 to 6; and d is 0 or 1;
(B) a compound which is compatible with or dispersible in ingredient (A) and has a boiling point or decomposition temperature of from 250 to 450xc2x0 C.; and
(C) an organic solvent.
The invention further provides a method of film formation which comprises applying the composition for film formation described above to a substrate and then heating the resulting coating.
The invention furthermore provides a silica-based film obtained by the method of film formation described above.